Chapter 6.3 DESCRIBING ACIDS AND BASES I. What Are the Properties of Acids? I. An Acid reacts with metals, reacts wth carbonates, tastes sour, and turns blue litmus paper red. A. REACTIONS WITH METALS Acids react with certain metals to produce hydrogen gas. The metals seem to disappear in the solution. This is one reason acids are described as corrosive, meaning they wear away other materials. B. REACTIONS WITH CARBONATES Carbonate ions contain carbon and oxygen atoms bonded together with an overall negative charge (CO3 2- ). One product of the reaction of an acid with carbonate is carbon dioxide. C. SOUR TASTE Citric acid (lemons, oranges, tomatoes, grapefruits) tastes sour. Other foods such as vinegar (acetic acid) and tomatoes (ascorbic acid) also contain acid. D. REACTIONS WITH INDICATORS Litmus paper is an example of an indicator, a compound that changes color when it comes in contact with an acid. Acid turns blue litmus paper red.
II. What Are the Properties of Bases? I. A Base tastes bitter, feels slippery, and turns red litmus paper blue. A. BITTER TASTE Tonic water, almonds and cocoa beans all contain bases that cause the sightly bitter taste. B. SLIPPERY FEEL Many soaps and detergents contain bases. Strong bases can irritate your skin. C. REACTIONS OF BASES Bases don t react with metals and they don t react with carbonate to form CO2. Bases react with acids in a type of chemical reaction called neutralization, in which acids and bases deactivate each other. D. REACTIONS WITH INDICATORS Litmus paper can be used to test bases. Bases turn red litmus paper blue.
6.4 Acids and Bases in Solution What Ions Do Acids and Bases Form in Water? I. Some common acids: HCl, HNO3, H2SO4, HC2H3O2. Each formula begins with the letter H, the symbol for Hydrogen. II. Some common bases: NaOH, KOH, Ca(OH)2, NH3. Many of the formulas for a base end with OH, the symbol for hydroxide. A. ACIDS IN SOLUTION In solution with water, acids separate into hydrogen ions and negative ions. A Hydrogen Ion (H+) is an atom of hydrogen that has lost its electrons. In the case of hydrochloric acid, hydrogen ions and chloride ions form: HCl (aq) H + + Cl - An acid produces hydrogen ions (H+) in water. Acids may be strong or weak. Strength refers to how well the acid dissociates, or separates, into ions in water. B. BASES IN SOLUTION When some bases dissolve in water they separate into positive ions and hydroxide ions (OH - ). C. NaOH Na + + OH -
Not every base contains hydroxide ions. In solution, ammonia (NH3) reacts with water to form hydroxide ions. NH3 + H2O NH4 + + OH - A base produces hydroxide ions (OH - ) in water. Bases may be strong or weak. Hydroxide ions are responsible for the bitter taste and slippery feel of bases. D. Measuring ph To determine the strength of an acid or base chemists use a scale called ph. The ph scale ranges from 0-14. It expresses the concentration of hydrogen ions in a solution. A ph lower than 7 is acidic. A ph higher than 7 is basic. If the ph is 7, the solution is neutral, meaning that is neither an acid or a base. III. What are the products of Neutralization? A reaction between an acid and a base is called neutralization. HCl + NaOH H2O + Na + + Cl - (acid) (base) (water) (salt) The ph of the resulting mixture would be close to 7. To a chemist the word salt refers to a specific group of compounds. A salt is any ionic compound that can be made from a neutralization reaction. In a neutralization reaction, an acid reacts with a base to produce a salt and water.
6.3 & 6.4 Exit Ticket 1. What is a concentrated solution? 2. CALCULATE Find the concentration of a solution with 30 grams of solute in 250 grams of solution. 3. I know that the concentration of a solution can be changed by.. 6.2 Exit Ticket 1. What is a concentrated solution? 2. CALCULATE Find the concentration of a solution with 30 grams of solute in 250 grams of solution. 3. I know that the concentration of a solution can be changed by..